Question

What happened when Eastern European countries, like Czechoslovakia, tried to reform and loosen communist restrictions during the 1960s-1970s?

the Soviet Union sent their troops to end the reforms and punish those leading the calls for changes

the Soviet Union bombed the major cities of those countries

the Soviet Union called for emergency meetings with communist leaders in Eastern Europe and removed those people who were calling for change

the Soviet Union did nothing and those countries continued with their changes